Overview
- It is the heaviest internal organ and largest gland in the body, weighing about 1.2 – 1.5 kg in an adult human.
- It is located in the upper right side of the abdominal cavity and is reddish brown in colour.
- It has two main lobes (larger right lobe & smaller left lobe) and two small lobes (quadrate lobe & caudate lobe) present behind the main lobes.
- The two main right and left lobes are separated by the falciform ligament.
- The liver consists of small structural and functional units called hepatic lobules.
- The lobules are roughly hexagonal, and consist millions of glycogen-rich cells, the hepatocytes (hepatic cells).
- Each lobule is covered by a thin connective tissue sheath known as Glisson’s capsule.
- The mammalian liver also contains phagocytic cells known as Kupffer cells. They engulf dead WBCs, RBCs and pathogens.
- A thin-walled, sac like structure, the gall bladder, lies in the lower surface of the right lobe. It stores and concentrates bile secreted by the liver cells.
- The duct of gall bladder is called cystic duct.
- The cystic duct is connected with common hepatic duct to form bile duct which passes downward and is joined by the pancreatic duct to form hepatopancreatic duct.
- The hepatopancreatic duct is connected with duodenum through a hepatopancreatic ampulla which is guarded by a sphincter called the sphincter of Oddi.
- There are two distinct sources that supply blood to the liver: oxygenated blood flows in, from the hepatic artery and nutrient-rich (deoxygenated) blood flows in, from the hepatic portal vein.
Fig: Liver and pancreas with their ducts.
Vital Functions
- Filtration of blood coming from the digestive tract, before passing it to the rest of the body.
- Regulation of blood sugar level through glycogenesis (conversion of excess glucose into glycogen) and glycogenolysis (conversion of glycogen into glucose).
- Performs gluconeogenesis (formation of glucose from non-carbohydrate source).
- Controls lipogenesis (conversion of excess glucose and amino acids into fats).
- Acts as haemolytic organ (breaks old RBCs).
- Secretes angiotensinogen, that later forms angiotensin – a peptide hormone and a potent dipsogen (agent that causes thirst). Angiotensin is also a part of renin-angiotensin system (a hormone system that regulates blood pressure and fluid balance).
- Detoxifies chemicals and metabolizes drugs.
- Secretes bile – an alkaline fluid having several organic and inorganic salts that helps in the emulsification of fats.
- Storage of glucose in the form of glycogen, mineral like copper, iron etc as well storage of vitamins like vitamin A, D, E, K and B12.